Method of quasi-atomic layer etching of silicon nitride

ABSTRACT

A method of etching is described. The method includes providing a substrate having a first material containing silicon nitride and a second material that is different from the first material, forming a first chemical mixture by plasma-excitation of a first process gas containing H and optionally a noble gas, and exposing the first material on the substrate to the first chemical mixture. Thereafter, the method includes forming a second chemical mixture by plasma-excitation of a second process gas containing S and F, and optionally a noble element, and exposing the first material on the substrate to the second plasma-excited process gas to selectively etch the first material relative to the second material.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application claims the benefit of U.S. Provisional PatentApplication No. 62/462,764, filed on Feb. 23, 2017, entitled “METHOD OFQUASI-ATOMIC LAYER ETCHING OF SILICON NITRIDE” which is incorporatedherein by reference in its entirety.

FIELD OF INVENTION

The invention relates to a method for etching, and more particularly, aprecision etch technique for etching a thin film for electronic deviceapplications.

BACKGROUND OF THE INVENTION

The present invention relates to a method of manufacturing asemiconductor device such as an integrated circuit and transistors andtransistor components for an integrated circuit. In the manufacture of asemiconductor device (especially on the microscopic scale), variousfabrication processes are executed such as film-forming depositions,etch mask creation, patterning, material etching and removal, and dopingtreatments, are performed repeatedly to form desired semiconductordevice elements on a substrate. Historically, with microfabrication,transistors have been created in one plane, with wiring/metallizationformed above, and have thus been characterized as two-dimensional (2D)circuits or 2D fabrication. Scaling efforts have greatly increased thenumber of transistors per unit area in 2D circuits, yet scaling effortsare running into greater challenges as scaling enters single digitnanometer semiconductor device fabrication nodes. Semiconductor devicefabricators have expressed a desire for three-dimensional (3D)semiconductor devices in which transistors are stacked on top of eachother.

As device structures densify and develop vertically, the need forprecision material etch becomes more compelling. Trade-offs betweenselectivity, profile, ARDE (aspect ratio dependent etching), anduniformity in plasma etch processes become difficult to manage. Currentapproaches to patterning and pattern transfer by balancing thesetrade-offs is not sustainable. The root cause for these trade-offs isthe inability to control ion energy, ion flux, and radical fluxindependently. However, self-limiting processes, such as atomic layeretching (ALE), offer a viable route to escape these trade-offs bydecoupling the etch process into sequential steps of surfacemodification and removal of modified surface regions, thereby allowingthe segregation of the roles of radical flux and ion flux and energy.

SUMMARY

Techniques herein pertain to device fabrication using precision etchtechniques.

A method of etching is described. The method includes providing asubstrate having a first material containing silicon nitride and asecond material that is different from the first material, forming afirst chemical mixture by plasma-excitation of a first process gascontaining H and optionally a noble gas, and exposing the first materialon the substrate to the first chemical mixture. Thereafter, the methodincludes forming a second chemical mixture by plasma-excitation of asecond process gas containing S and F, and optionally a noble element,and exposing the first material on the substrate to the secondplasma-excited process gas to selectively etch the first materialrelative to the second material.

Another method of etching is described. The method includes providing asubstrate having a first material containing silicon nitride and asecond material that is different from the first material, forming afirst chemical mixture by plasma-excitation of a first process gascontaining H and optionally a noble gas, and exposing the first materialon the substrate to the first chemical mixture. Thereafter, the methodincludes forming a second chemical mixture by plasma-excitation of asecond process gas containing a high fluorine content molecule, andoptionally a noble element, wherein the ratio of fluorine to otheratomic elements of the high fluorine content molecule exceeds unity, andexposing the first material on the substrate to the secondplasma-excited process gas to selectively etch the first materialrelative to the second material.

Of course, the order of discussion of the different steps as describedherein has been presented for clarity sake. In general, these steps canbe performed in any suitable order. Additionally, although each of thedifferent features, techniques, configurations, etc. herein may bediscussed in different places of this disclosure, it is intended thateach of the concepts can be executed independently of each other or incombination with each other. Accordingly, the present invention can beembodied and viewed in many different ways.

Note that this summary section does not specify every embodiment and/orincrementally novel aspect of the present disclosure or claimedinvention. Instead, this summary only provides a preliminary discussionof different embodiments and corresponding points of novelty overconventional techniques. For additional details and/or possibleperspectives of the invention and embodiments, the reader is directed tothe Detailed Description section and corresponding figures of thepresent disclosure as further discussed below.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIG. 1 illustrates a schematic representation of a method of etching athin film on a substrate according to an embodiment;

FIG. 2 provides a flow chart illustrating a method of etching asubstrate according to an embodiment;

FIG. 3 illustrates a result obtained using the method of etchingdepicted in FIGS. 1 and 2;

FIGS. 4 and 5 illustrate additional results obtained using the method ofetching depicted in FIGS. 1 and 2;

FIGS. 6A through 6D illustrate various exemplary fabrication sequencesto which the method of etching depicted in FIGS. 1 and 2 can be appliedaccording to several embodiments;

FIGS. 7A and 7B illustrate a schematic representation of a method ofetching a thin film on a substrate according to another embodiment;

FIG. 8 provides a flow chart illustrating a method of etching asubstrate according to yet another embodiment; and

FIGS. 9A through 9D provide schematic illustrations of plasma processingsystems for performing the method of etching according to variousembodiments.

DETAILED DESCRIPTION

Techniques herein pertain to device fabrication using precision etchtechniques. Several instances manifest in semiconductor manufacturing inboth front end of line (FEOL, e.g., transistor fabrication) through tothe back end of line (BEOL, e.g., interconnect fabrication), where oxideand nitride films (typically silicon-containing, in nature) need to beetched with a high degree of precision.

Numerous fabrication sequences in semiconductor manufacturing demandprecision etch techniques. Examples, which will be discussed later,include: (1) gate spacer etch for both 2D (two-dimensional) and 3D(three-dimensional) device structures, (2) spacer etch for sidewallimage transfer (SIT) for multi-patterning, (3) mandrel removal from apost-spacer etch SIT structure, and (4) liner etch from a raisedstructure.

As another example, fabrication of self-aligned block (SAB) structureshas become a critical step in self-aligned double patterning (SADP),self-aligned quadruple patterning (SAQP), and other variations ofself-aligned multiple patterning (SAMP). As part of an SAB flow, asilicon nitride mandrel is anisotropically etched with selectivity to anoxide spacer. Current approaches to etch silicon nitride mandrel do nothave the required selectivity, which exceeds 15 (i.e., the etch rate ofsilicon nitride is 15 times greater than the etch rate of silicon oxide)to etch the mandrel without damaging the oxide spacer.

This invention relates to development of an anisotropic process that canetch silicon nitride mandrel with extremely high selectivity (e.g., >15,or >20, or >30, or >50, or >80, and even >100) to oxide spacer, therebyenabling SAB fabrication flows.

According to several embodiments, FIGS. 1 and 2 illustrate a method ofetching a thin film. The method, depicted as flow chart 200, includesproviding a substrate having a first material 100 containing siliconnitride and a second material (not shown) that is different from thefirst material 100, forming a first chemical mixture byplasma-excitation of a first process gas containing H and optionally anoble gas in step 210, and exposing the first material on the substrateto the first chemical mixture in step 220, the combination of which isdepicted as 102 in FIG. 1. Thereafter, the method includes forming asecond chemical mixture by plasma-excitation of a second process gascontaining N, F, and O, and optionally a noble element in step 230, andexposing the first material 100 on the substrate to the secondplasma-excited process gas to selectively etch the first material 100relative to the second material in step 240, the combination of which isdepicted as 104 in FIG. 1. Alternatively, the method includes forming asecond chemical mixture by plasma-excitation of a second process gascontaining S and F, and optionally a noble element in step 230, andexposing the first material 100 on the substrate to the secondplasma-excited process gas to selectively etch the first material 100relative to the second material in step 240, the combination of which isdepicted as 104 in FIG. 1.

The first material 100, to be etched, contains, consists essentially of,or consists of silicon nitride, expressed as Si₃N₄, or more genericallySi_(x)N_(y), wherein x and y are real number greater than zero. Thesecond material (not shown) can include silicon oxide, e.g., SiO₂, orother silicon-containing material, a metal or metal-containing material,or an organic material, such as an organic planarization layer (OPL),resist, or antireflective coating (ARC).

As set forth above, the first chemical mixture is formed from the plasmaexcitation of a first process gas. The first process gas containshydrogen (H), and can include atomic hydrogen (H), molecular hydrogen(H₂), metastable hydrogen, hydrogen radical, or hydrogen ions, or anycombination of two or more thereof. In one embodiment, the first processgas includes H₂, or H₂ and Ar. In another embodiment, the first processgas consists essentially of or consists of H₂. In yet anotherembodiment, the first process gas consists essentially of or consists ofH₂ and Ar.

As also set forth above, the second chemical mixture is formed from theplasma excitation of a second process gas. The second process gas cancontain a high fluorine content molecule, wherein the ratio of fluorineto other atomic elements exceeds unity. The second process gas cancontain nitrogen (N), fluorine (F), and oxygen (O), and can optionallyinclude a noble element, such as Ar (argon). In one embodiment, thesecond process gas includes NF₃, O₂, and Ar. In another embodiment, thesecond process gas consists essentially of or consists of NF₃, O₂, andAr. Alternatively, the second process gas can contain sulfur (S) andfluorine (F), and can optionally include a noble element, such as Ar(argon). In one embodiment, the second process gas includes SF₆ and Ar.In another embodiment, the second process gas consists essentially of orconsists of SF₆ and Ar.

The plasma-excitation of the first process and/or the second process gascan be performed in-situ (i.e., the first and/or second chemical mixtureis formed within a gas-phase, vacuum environment in proximate contactwith the substrate), or ex-situ (i.e., the first and/or second chemicalmixture is formed within a gas-phase, vacuum environment remotelylocated relative to the substrate). FIGS. 9A through 9D provide severalplasma generating systems that may be used to facilitateplasma-excitation of a process gas. FIG. 9A illustrates a capacitivelycoupled plasma (CCP) system, wherein plasma is formed proximate asubstrate between an upper plate electrode (UEL) and a lower plateelectrode (LEL), the lower electrode also serving as an electrostaticchuck (ESC) to support and retain the substrate. Plasma is formed bycoupling radio frequency (RF) power to at least one of the electrodes.As shown in FIG. 9A, RF power is coupled to both the upper and lowerelectrodes, and the power coupling may include differing RF frequencies.Alternatively, multiple RF power sources may be coupled to the sameelectrode. Moreover, direct current (DC) power may be coupled to theupper electrode.

FIG. 9B illustrates an inductively coupled plasma (ICP) system, whereinplasma is formed proximate a substrate between an inductive element(e.g., a planar, or solenoidal/helical coil) and a lower plate electrode(LEL), the lower electrode also serving as an electrostatic chuck (ESC)to support and retain the substrate. Plasma is formed by coupling radiofrequency (RF) power to the inductive coupling element. As shown in FIG.9B, RF power is coupled to both the inductive element and lowerelectrode, and the power coupling may include differing RF frequencies.

FIG. 9C illustrates a surface wave plasma (SWP) system, wherein plasmais formed proximate a substrate between a slotted plane antenna and alower plate electrode (LEL), the lower electrode also serving as anelectrostatic chuck (ESC) to support and retain the substrate. Plasma isformed by coupling radio frequency (RF) power at microwave frequenciesthrough a waveguide and coaxial line to the slotted plane antenna. Asshown in FIG. 9C, RF power is coupled to both the slotted plane antennaand lower electrode, and the power coupling may include differing RFfrequencies.

FIG. 9D illustrates remote plasma system, wherein plasma is formed in aregion remote from a substrate and separated from the substrate by afilter arranged to impede the transport of charged particles from theremote plasma source to a processing region proximate the substrate. Thesubstrate is supported by a lower plate electrode (LEL) that also servesas an electrostatic chuck (ESC) to retain the substrate. Plasma isformed by coupling radio frequency (RF) power to a plasma generatingdevice adjacent the remotely located region. As shown in FIG. 9D, RFpower is coupled to both the plasma generating device adjacent theremote region and lower electrode, and the power coupling may includediffering RF frequencies.

The plasma processing systems of FIGS. 9A through 9D are intended to beillustrative of various techniques for implementing the steppedion/radical process described. Other embodiments are contemplatedincluding both combinations and variations of the systems described.

When forming the first chemical mixture by plasma-excitation of thefirst process gas containing H and optionally a noble gas, and exposingthe first material on the substrate to the first chemical mixture, thegas pressure for the exposing can be less than or equal to 100 mTorr.For example, the gas pressure may range from 20 mTorr to 100 mTorr.Additionally, the substrate may be electrically biased by coupling RFpower to the lower plate electrode (LEL). RF power may or may not alsobe applied to the plasma generating device.

When forming the second chemical mixture by plasma-excitation of thesecond process gas containing N, F, and O (or S and F), and optionally anoble gas, and exposing the second material on the substrate to thesecond chemical mixture, the gas pressure for the exposing can begreater than or equal to 100 mTorr. For example, the gas pressure mayrange from 100 mTorr to 1000 mTorr. Additionally, the substrate may beelectrically biased by coupling RF power to the lower plate electrode(LEL). RF power may or may not also be applied to the plasma generatingdevice.

Turning now to FIG. 3 and Table 1, a silicon nitride film, deposited bychemical vapor deposition (CVD) (CVD SiN), is exposed to several etchingprocesses together with an adjacent silicon oxide film. In a firstexample, the two films are exposed to a hydrogen (H₂) plasma only,according to the conditions provided in Table 1. In this ion-drivenhydrogen plasma, the two films are not etched and no selectivity betweenfilms is observed. In a second example, the two films are exposed toplasma composed of NF₃, O₂, and Ar. In this radical-driven plasma,eleven (11) Angstroms are etched from the silicon nitride film and onlyone (1) Angstrom is etched from the silicon oxide film, thus, leading toan etch selectivity of 11-to-1. In a third example, the two films aresequentially exposed to the hydrogen (H₂) plasma, and then exposed tothe plasma composed of NF₃, O₂, and Ar. In this ion and radical-drivensequential plasma, sixty one (61) Angstroms are etched from the siliconnitride film and substantially no etching is observed of the siliconoxide film, thus, leading to an etch selectivity exceeding 60-to-1.

TABLE 1 Tool: CCP, ICP, RLSA H2 plasma: 20-100 mT, HF 0 W, LF 25-100 W,500H2/50 Ar, 15C, 15-60 sec NF3—O2 plasma: 100-500 mT, HF 0-1000 W, LF15-100 W, 480NF3/160O2/1000 Ar, 15C, 5-60 sec Dominant plasma EtchAmount [Å] Selectivity Step species CVD SiN Oxide SiN-Oxide H2 plasmaonly Ion- −0.6 −3 No driven sputtering NF3—O2 plasma only Radical- 111 >11 driven H2 + NF3—O2 plasma 61 −1 >60

In a fourth example, the two films are exposed to plasma composed of SF₆and Ar. In this radical-driven plasma, about twenty (20) Angstroms areetched from the silicon nitride film. In a fifth example, the two filmsare sequentially exposed to the hydrogen (H₂) plasma, and then exposedto the plasma composed of SF₆ and Ar. In this radical and ion-drivensequential plasma, about one hundred thirty eight (138) Angstroms areetched from the silicon nitride.

The inventors surmise that hydrogen ions during the hydrogen plasma stepenrich a surface region of the silicon nitride and the silicon oxide,leading to elevated sub-surface hydrogen concentrations; see FIGS. 4 and5. As shown in FIG. 5, the hydrogen content increases in region 1(heavily modified sub-surface region) to a maximum, then decays throughmoderate concentration levels in region 2 (moderately modifiedsub-surface region), until it decays to low levels in region 3 (pristineor original material). Then, the NF₃ and O₂ plasma, or SF₆ and Arplasma, creates radicals that selectively react with the hydrogenatedsilicon nitride and volatilize at a rate greater than with the secondmaterial, e.g., silicon oxide or organic material. FIG. 3 illustratesthe etch amounts achieved with each exemplary process. And, as shown inFIG. 4, the etch amount achieved during the NF₃ and O₂, or SF₆ and Ar,step decreases (or the etch rate decays) as the etching proceeds throughthe sub-surface regions from relatively high hydrogen concentration torelatively low hydrogen concentration.

In FIGS. 6A through 6D, several examples of fabrication sequences insemiconductor manufacturing that demand precision etch techniques areprovided. In each example, it is necessary to remove silicon nitridewith high selectivity to other materials, and the examples include: (1)gate spacer etch for both 2D (two-dimensional) and 3D(three-dimensional) device structures, (2) spacer etch for sidewallimage transfer (SIT) for multi-patterning, (3) mandrel removal from apost-spacer etch SIT structure, and (4) liner etch from a raisedstructure. FIG. 6A illustrates selectively removing a silicon nitride615 from the cap region of the gate structure 610. FIG. 6B illustratesselectively removing a silicon nitride 625 from a cap region and footerregion surrounding a mandrel 620 utilized in a self-alignedmulti-patterning (SAMP) scheme. FIG. 6C illustrates selectively removinga silicon nitride mandrel 635 from a post-spacer etch structure 630 toleave behind double patterned spacer structures. FIG. 6D illustratesselectively removing silicon nitride liners 645 to leave behind a raisedfeature 640.

In yet another example, the fabrication of self-aligned block (SAB)structures has become a critical step in self-aligned double patterning(SADP), self-aligned quadruple patterning (SAQP), and other variationsof self-aligned multiple patterning (SAMP). As part of an SAB flow, asilicon nitride mandrel is anisotropically etched with selectivity to anoxide spacer. Current approaches to etch silicon nitride mandrel do nothave the required selectivity, which exceeds 15 (i.e., the etch rate ofsilicon nitride is 15 times greater than the etch rate of silicon oxide)to etch the mandrel without damaging the oxide spacer.

As shown in FIG. 7A, a substrate 700 can include a patterned layer 720overlying a film stack 710, including one or more optional layers 712,714, 716 to be etched or patterned. The patterned layer 720 can definean open feature pattern overlying one or more additional layers. Thesubstrate 700 further includes device layers. The device layers caninclude any thin film or structure on the workpiece into which a patternis to be transferred, or a target material is to be removed.Furthermore, the patterned layer 720 can include a retention layer 722,and a target layer 724 to be removed.

The target layer 724 can be composed of silicon nitride. As shown inFIGS. 7A and 7B, the target layer 724 fills a trench or via 725 withinretention layer 722, the trench or via 725 has a depth (D) 727, a width(W) 726, and an aspect ratio (D/W). The aspect ratio can be greater than3, 4, or 5. For some structures, the aspect ratio can be greater than10, 15, or even 20. The width (W) 726 can be less than 50 nm, 40 nm, 30nm, or 20 nm. In some applications, the width (W) 726 is less than 10nm. The retention layer 722 can be composed of material selected fromthe group consisting of silicon oxide (SiO_(x)), silicon oxynitride(SiO_(x)N_(y)), transition metal oxide (e.g., titanium oxide (TiO_(x))),transition metal nitride (e.g., titanium nitride (TiN_(y))), andsilicon-containing organic material having a silicon content rangingfrom 15% by weight to 50% by weight silicon.

As an example, the patterned layer 720 in FIG. 7A can include a spacerlayer surrounding a mandrel layer used in multi-patterning schemes.Alternatively, for example, the patterned layer 720 in FIG. 7A caninclude a dummy silicon nitride layer filling a region to be replacedwith an advanced gate structure, such as a metal gate structure.

The substrate 700 can include a bulk silicon substrate, a single crystalsilicon (doped or un-doped) substrate, a semiconductor-on-insulator(SOI) substrate, or any other semiconductor substrate containing, forexample, Si, SiC, SiGe, SiGeC, Ge, GaAs, InAs, InP, as well as otherIII/V or II/VI compound semiconductors, or any combination thereof(Groups II, III, V, VI refer to the classical or old IUPAC notation inthe Periodic Table of Elements; according to the revised or new IUPACnotation, these Groups would refer to Groups 2, 13, 15, 16,respectively). The substrate 700 can be of any size, for example, a 200mm (millimeter) substrate, a 300 mm substrate, a 450 mm substrate, or aneven larger substrate. The device layers can include any film or devicestructure into which a pattern can be transferred.

Organic layer 721 blankets various regions of substrate 700, and exposesblock regions within which the silicon nitride mandrel is to be removedfrom high aspect ratio features. In FIG. 7B, the silicon nitride mandrel714 is selectively removed with minimal impact to the silicon oxidespacers and the organic layer 721.

FIG. 8 depicts a flow chart 800 for etching a substrate according toanother embodiment. In 810, a self-aligned block (SAB) structure isprepared. And, in 820, a mandrel is removed from an exposed region ofthe SAB structure. FIG. 8 depicts a method of selectively etching asilicon nitride mandrel from a high aspect ratio feature to leave behindsilicon oxide spacers. The aspect ratio can exceed ten (10, and the etchselectivity for removing the silicon nitride mandrel relative to othermaterials, e.g., silicon oxide and organic material, can exceed 20-to-1,or 50-to-1, or even 100-to-1.

In the claims below, any of the dependents limitations can depend fromany of the independent claims.

In the preceding description, specific details have been set forth, suchas a particular geometry of a processing system and descriptions ofvarious components and processes used therein. It should be understood,however, that techniques herein may be practiced in other embodimentsthat depart from these specific details, and that such details are forpurposes of explanation and not limitation. Embodiments disclosed hereinhave been described with reference to the accompanying drawings.Similarly, for purposes of explanation, specific numbers, materials, andconfigurations have been set forth in order to provide a thoroughunderstanding. Nevertheless, embodiments may be practiced without suchspecific details. Components having substantially the same functionalconstructions are denoted by like reference characters, and thus anyredundant descriptions may be omitted.

Various techniques have been described as multiple discrete operationsto assist in understanding the various embodiments. The order ofdescription should not be construed as to imply that these operationsare necessarily order dependent. Indeed, these operations need not beperformed in the order of presentation. Operations described may beperformed in a different order than the described embodiment. Variousadditional operations may be performed and/or described operations maybe omitted in additional embodiments.

“Substrate” or “target substrate” as used herein generically refers toan object being processed in accordance with the invention. Thesubstrate may include any material portion or structure of a device,particularly a semiconductor or other electronics device, and may, forexample, be a base substrate structure, such as a semiconductor wafer,reticle, or a layer on or overlying a base substrate structure such as athin film. Thus, substrate is not limited to any particular basestructure, underlying layer or overlying layer, patterned orun-patterned, but rather, is contemplated to include any such layer orbase structure, and any combination of layers and/or base structures.The description may reference particular types of substrates, but thisis for illustrative purposes only.

Those skilled in the art will also understand that there can be manyvariations made to the operations of the techniques explained abovewhile still achieving the same objectives of the invention. Suchvariations are intended to be covered by the scope of this disclosure.As such, the foregoing descriptions of embodiments of the invention arenot intended to be limiting. Rather, any limitations to embodiments ofthe invention are presented in the following claims.

The invention claimed is:
 1. A method of etching, comprising: providinga substrate having a first material containing silicon nitride and asecond material that is different from the first material with thesecond material provided along first and second side walls of the firstmaterial such that the first material is between the second material onthe first and second side walls and the first material fills a regionbetween the second material on the first and second side walls; forminga first chemical mixture by plasma-excitation of a first process gascontaining H and optionally a noble gas; exposing the first material onthe substrate to the first chemical mixture to hydrogenate a surface andsubsurface regions of the first material, the subsurface regionsincluding a first portion and a second portion below the first portion,and after the exposing first material to the first chemical mixture thefirst portion has a hydrogen concentration greater than that at thesurface and the second portion has a hydrogen concentration lower thanthat at the surface; thereafter, forming a second chemical mixture byplasma-excitation of a second process gas containing S and F, andoptionally a noble element; exposing the first material on the substrateto the second plasma-excited process gas to selectively etch the firstmaterial relative to the second material; and repeating the exposing thefirst material to the first chemical mixture and the exposing the firstmaterial to the second plasma-excited process gas to remove the firstmaterial between the second material until a layer positioned under thefirst material is exposed, and after the layer positioned under thefirst material is exposed, the second material remains on the substrate.2. The method of claim 1, wherein the first process gas contains H₂. 3.The method of claim 1, wherein the first process gas consists of H₂. 4.The method of claim 1, wherein the first process gas consists of H₂ andAr.
 5. The method of claim 1, wherein the second process gas containsSF₆ and Ar.
 6. The method of claim 1, wherein the second process gasconsists of SF₆ and Ar.
 7. The method of claim 1, wherein the firstchemical mixture contains hydrogen ions.
 8. The method of claim 1,wherein the second chemical mixture contains substantiallycharge-neutral species.
 9. The method of claim 1, wherein the secondmaterial is selected from the group consisting of SiO₂ and organicmaterials.
 10. The method of claim 1, wherein the plasma excitation ofthe first process gas or the second process gas includes generatingplasma using a capacitively coupled plasma source containing an upperplate electrode, and a lower plate electrode supporting the substrate.11. The method of claim 1, wherein the plasma excitation of the firstprocess gas or the second process gas includes generating plasma usingan inductively coupled plasma source containing an inductive element,and a lower plate electrode supporting the substrate.
 12. The method ofclaim 1, wherein the plasma excitation of the first process gas or thesecond process gas includes generating plasma using a remote plasmasource that creates a high radical to ion flux ratio.
 13. The method ofclaim 1, wherein the first material is removed at an etch selectivity ofgreater than 100-to-1 relative to the second material.
 14. The method ofclaim 1, wherein the first material is a mandrel in a self-alignedmulti-patterning (SAMP) process.
 15. The method according to claim 1,further including: performing the exposing the first material to thefirst chemical mixture in a processing chamber at a first pressure,performing the exposing the first material to the second plasma-excitedprocess gas in the processing chamber at a second pressure, and thesecond pressure is greater than the first pressure; and wherein thefirst process gas consists essentially of hydrogen and optionally anoble gas.
 16. The method according to claim 15, wherein during theexposing the first material to the first chemical mixture, a flow offluorine containing gas to the processing chamber is turned off.
 17. Amethod of etching, comprising: providing a substrate having a firstmaterial containing silicon nitride and a second material that isdifferent from the first material with the second material providedalong first and second side walls of the first material such that thefirst material is between the second material on the first and secondside walls and the first material fills a region between the secondmaterial on the first and second side walls; forming a first chemicalmixture by plasma-excitation of a first process gas containing H andoptionally a noble gas; exposing the first material on the substrate tothe first chemical mixture to hydrogenate a surface and subsurfaceregions of the first material, the subsurface regions including a firstportion and a second portion below the first portion, and after theexposing first material to the first chemical mixture the first portionhas a hydrogen concentration greater than that at the surface and thesecond portion has a hydrogen concentration lower than that at thesurface; thereafter, forming a second chemical mixture byplasma-excitation of a second process gas containing a high fluorinecontent molecule, and optionally a noble element, wherein the ratio offluorine to other atomic elements of the high fluorine content moleculeexceeds unity; exposing the first material on the substrate to thesecond plasma-excited process gas to selectively etch the first materialrelative to the second material; and repeating the exposing the firstmaterial to the first chemical mixture and the exposing the firstmaterial to the second plasma-excited process gas to remove the firstmaterial between the second material until a layer positioned under thefirst material is exposed, and after the layer positioned under thefirst material is exposed, the second material remains on the substrate.18. The method according to claim 17, further including: performing theexposing the first material to the first chemical mixture in aprocessing chamber at a first pressure, performing the exposing thefirst material to the second plasma-excited process gas in theprocessing chamber at a second pressure, and the second pressure isgreater than the first pressure; and wherein the first process gasconsists essentially of hydrogen and optionally a noble gas.
 19. Themethod according to claim 18, wherein during the exposing the firstmaterial to the first chemical mixture, a flow of fluorine containinggas to the processing chamber is turned off.